信号增强装置问题要求对于一个给定的信号传输网络，计算如何放置最少的信号增强装置来保证网络传输的畅通。

对于给定的带权树，计算放置信号增强装置最少数量。

-Signal enhancement device for a given problem requires the signal transmission network, calculating how to place a minimum of signal enhancement device to ensure the smooth flow of network traffic. For a given weighted tree, calculate the minimum number of devices placed on signal enhancement.